Microstructured belt contact surface

ABSTRACT

A transport belt, in particular for machines for the production of web material such as paper or paperboard, has, on a web material contact side, depressions of which the majority has a depression opening with a dimension smaller than 20 μm in at least one direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 10 2006 003 706.5 filed Jan. 26, 2006, the disclosure of which is expressly incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a transport belt that can be used on machines for the production of web material, for example paper or paperboard.

2. Background Description

From U.S. Pat. No. 6,331,231 B1 there is known a transport belt for paper machines which has, on a web material contact side provided to come into contact with a web material to be produced or processed, depressions in a surface otherwise constructed to be flat. These depressions are generated by inserting so-called microcapsules, which have a diameter in the range from 20 μm to 40 μm, into the construction material. After finishing of the transport belt the microcapsules positioned near the surface lead to depressions in the belt. Depending on the position of the microcapsules in the surrounding material of the transport belt, the depressions have a depression opening whose dimension is equal at most to the diameter of the microcapsules used (namely when said microcapsules are embedded by exactly half in the surrounding material). In the case of microcapsules which are less deeply or more deeply embedded, the dimension of the depression opening is then smaller than the diameter of the microcapsules.

From U.S. Pat. No. 6,962,885 B1 there is known a transport belt for a paper machine which likewise has, on its web material contact side, depressions which are created by inserting particles into the construction material transport belt. Those particles which are not fully enclosed by the construction material are subsequently dissolved, leaving depressions whose shape and size depend on the extent to which the dissolved particles were embedded in the construction material. Given that the particles used are to have a diameter of 200 μm and less, the depression openings remaining after the particles are dissolved have dimensions equal to 200 μm and less.

During processing of the web material, liquid is pressed out of the web material from a surface region between the transport belt and the web material. By providing such depressions on the web material contact side of a transport belt an attempt is made to discharge at least a part of the liquid from the surface region between the transport belt and the web material, thus creating disturbances in a liquid film otherwise generated between these surfaces. As the result, an adhesive effect generated by a continuous liquid film in the region where the web material and the transport belt are separated from each other is reduced. However, a problem caused by such a surface structuring, by the introduction of such depressions is that the direct contact between the web material and the contact belt generates an accordingly structured image in the surface of the web material. In other words, the introduction of depressions produces a marking effect that may lead to impairments of quality.

SUMMARY OF THE INVENTION

The invention provides a transport belt, in particular for machines for the production of web material such as paper or paperboard, with which it is possible to lessen the problem of intensive adhesion between the web material and the transport belt essentially without impairing the quality of the finished web material.

According to the invention, a transport belt, in particular for machines for the production of web material such as paper or paperboard, has a web material contact side with depressions. A majority of the depressions has a depression opening with a dimension smaller than 20 μm in at least one direction.

As a basis of the current invention it is assumed that, for the production of web material such as paper or paperboard, a starting material is used which is essentially comprised of very small fibers. By providing depressions which, at least in one direction, are not wider than 20 μm, it is assured that the fibers contained in the web material are unable to submerge in said depressions. However, because the fibers have a larger cross-sectional dimension than the previously mentioned dimension of the depression openings, the fibers run over the depressions existing on the web material contact side. Hence the depressions are still able to pick up liquid and ensure that no excessively strong adhesive effect is generated upon separation of the web material from the transport belt, while at the same time the risk of the web material surface being marked by structuring of the transport belt can be greatly lessened.

In this case the tendency to marking can be reduced further or prevented essentially completely if, essentially with all depressions, the dimension of the depression opening is smaller than 20 μm at least in one direction.

Depending on the requirements and also, where applicable, on the web material to be produced, the depressions on the web material contact side can be arranged, at least in some regions, in an essentially regular pattern of depressions. Additionally, the depressions can be arranged, at least in some regions, in an irregular pattern of depressions. The depressions can be created by mechanical, thermal or chemical methods. Combinations of several of these methods are also possible of course. Calendaring, embossing, grinding or/and etching can be cited as examples in this connection.

Also, the invention relates to a method for the production of a material web, in particular paper or paperboard. With this method, use is made of a transport belt having depressions on a web material contact side. A depression opening of a majority of these depressions have a dimension, at least in one direction, is smaller than the diameter of the fibers contained in the web material to be produced.

Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.

BRIEF DESCRIPTION OF THE FIGURE

The current invention is further described the detailed description which follows. The present invention is described by way of a non-limiting example of the preferred embodiment of the present invention, wherein:

The FIGURE shows a partial sectional illustration of a transport belt according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

The FIGURE illustrates a transport belt 10 constructed according to the invention. The transport belt 10 has, in a central region, a reinforcement 12 which provides for the structural cohesion of the transport belt 10, and in particular the required tensile strength. The reinforcement 12 can comprise a fiber fabric or else a fiber material which is inserted or arranged in some other way. The fiber material or the reinforcement 12 is embedded in the construction material 14 of the transport belt. The construction material 14 can be, e.g., polyurethane. It is possible to construct the transport belt 10 from multiple layers and also to use different materials therefore. The materials can then be optimally selected for the respective requirements. For example, the construction material of the transport belt 10 which lies on the rear side (not illustrated) and comes in to contact with guide or drive elements can be selected with consideration to aspects of wear and aspects of durability. Additionally, while the construction material 14 provided on a web material contact side 16 can be selected above all with consideration to the fact that said material comes into contact with the web material to be produced and that certain properties are to evolve thereby.

On the web material contact side 16, the transport belt 10 has a web material contact surface 18. In this web material contact surface 18 there are depressions 20 which, in the region of the web material contact surface 18, open at a depression opening 22. Fibers 24, such as are contained in the web material to be produced and are pressed, above all when passing through a press nip, against the web material contact surface 18 of the transport belt 10, are shown in part above the depressions. Additionally, the depressions 20 are arranged a regular distance apart from each other. During contact, it is possible for liquid, which is contained in the web material to be produced and is pressed out due to the compressive load, to be picked up, at least partially, in the depressions 20. In this manner, development of a continuous and unwanted adhesive effect can be prevented through disturbances created in this water film, which guarantee easier releasing when the transport belt 10 separates from the web material.

From the FIGURE, it is evident that the depressions 20 have depression openings 22 with a dimension d which, at least in the direction evident in FIG. 1, is smaller than the diameter of the fibers 24. Thus, the fibers 24 can come to lie above the depressions 20 or the depression openings 22 but cannot submerge essentially into said depressions 20. Conversely, the material region 26 of the construction material 14 lying between two depressions 20 is unable to penetrate essentially into the web material which is to be produced or processed. Thus, unwanted marking of the web material by the surface texture of the transport belt 10 when passing through a press station can be largely prevented.

To achieve the previously described effect, it is advantageous for the depressions 20 to be designed such that the depression opening 22 has a dimension d which is smaller than 20 μm in at least one direction. The fibers contained in web material, such as paper or paperboard, generally have a diameter or mean diameter that is far larger than 20 μm. Hence the effect, illustrated in the FIGURE, of the fibers 24 essentially being unable to penetrate the depressions 20 can be assured through corresponding dimensioning of the depression opening 22. If the depressions 20 have a spherical dome shape for example, then the dimension d of the depression openings 22 can equal the diameter existing on the web material contact surface 18. However, the depressions 20 can also have any other shapes, for example groove-like or notch-like shapes. In each case steps must be taken to ensure, in accordance with the principle of the current invention, that the quoted dimension of 20 μm for example is not exceeded in one direction, which in the case of an elongated groove-like or notch-like depression 20 would be the width direction. In this case, even if a fiber extends exactly along a groove-like or notch-like depression, it is possible ensure that the fiber is unable, on account of the far larger fiber diameter, to submerge in the depression. In the case of fibers 24 which extend transversely to the extension of such elongated depressions, in other words fibers extending in the direction in which the depression opening 22 has this dimension of at most approximately 20 μm, there is similarly no risk of submerging.

The depressions 20 can be formed in the inventively constructed belt in various ways. For example, the transport belt 10 can be deformed in its region near the web material contact surface 18 by embossing or calendering methods performed by the surface structuring of calendar rollers for example. Also, surface depressions with the required dimension can be generated by etching operations or grinding operations. Furthermore, the depressions 20 can be provided not only in a regular arrangement as shown in FIG. 1, but also in an irregular arrangement or shape.

Finally it should be noted that where reference is made in connection with the current invention to essentially all depressions having the quoted dimension, even if an attempt is made during a production operation to avoid depressions with a larger opening dimension, it is impossible in principle to rule out that at least a small fraction of openings may exceed the quoted dimension on account of production tolerances which are always bound to exist. However, this will have no elementary effect on the quality of the web material produced therewith.

It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. 

1. A transport belt for machines for production of web material, comprising: a web material contact side having depressions, wherein a dimension of depression openings of a majority of the depressions is less than 20 μm in at least one direction.
 2. The transport belt according to claim 1, wherein the majority of the depressions is essentially all of the depressions.
 3. The transport belt according to claim 1, wherein the depressions on the web material contact side are arranged, at least in some regions, in an essentially regular pattern of depressions.
 4. The transport belt according to claim 1, wherein the depressions on the web material contact side are arranged, at least in some regions, in an irregular pattern of depressions.
 5. The transport belt according to claim 1, wherein the depressions are created by at least one of mechanical, thermal and chemical methods.
 6. The transport belt according to claim 1, wherein the web material is one of paper and paperboard.
 7. A method for producing a transport belt, comprising: forming depressions on a web material contact side of a belt, wherein at least one dimension of a depression opening for a majority of the depressions is smaller than a fiber diameter of fibers in a web material to be transported.
 8. The method according to claim 7, wherein the web material is one of paper and paperboard.
 9. The method according to claim 7, wherein the forming is by at least one of mechanical, thermal and chemical methods.
 10. The method according to claim 7, wherein the fiber diameter is greater than approximately 20 μm.
 11. The method according to claim 7, wherein the at least one dimension of the depression openings is less than 20 μm.
 12. A method for producing web material, comprising: forming depressions on a web material contact side of a transport belt, wherein at least one dimension of a depression opening for a majority of the depressions is smaller than a fiber diameter of fibers in a web material to be transported; and transporting the web material on the web material contact side of the transport belt.
 13. The method according to claim 12, wherein the web material is one of paper and paperboard.
 14. The method according to claim 12, wherein the forming is by at least one of mechanical, thermal and chemical methods.
 15. The method according to claim 12, wherein the fiber diameter is greater than approximately 20 μm.
 16. The method according to claim 12, wherein the at least one dimension of the depression openings is less than 20 μm.
 17. The method according to claim 12, further comprising: guiding the transport belt and the web material through a press nip. 